Method of mycophenolate mofetil preparation

ABSTRACT

Synthesis of mycophenolate mofetil (1), where R 1 =2-(-morpholinyl)ethyl and R 2 =hydrogen atom, includes reaction of mycophenolic acid with 4-(2-hydroxyethyl)morpholine in a suitable solvent under azeotropic separation of water.

FIELD OF THE INVENTION

This invention refers to method of mycophenolate mofetil preparationaccording to the formula I

where

-   R¹ is 2-(4-morpholinyl)ethyl,-   R² is hydrogen atom.

Mycophenolate mofetil (I) is used as an immunosuppressive forprophylactic treatment in combination with other immunosuppressives(cyclosporine A, prednisone), or for treatment of refractory rejectionsin patients after renal transplantation. Chemically, mycophenolatemofetil is 2-(4-morpholinyl)ethyl ester of mycophenolic acid (R¹=R²=H),which has cytostatic effect. It carries out inosine monophosphatedehydrogenaze selective inhibition, and this way also de novo synthesispathway of guanosine nucleotides and their incorporation into DNK. Thisway cytostatic effect to lymphocytes is higher that to other cells.

BACKGROUND ART

Synthesis of mycophenolate mofetil in accordance with the formula I(R¹=2-morpholinoethyl, R²═H) is described in the basic patent EP 281 713B1 (1987) and several other patents: U.S. Pat. No. 4,808,592 (1989),U.S. Pat. No. 4,753,935 (1988), U.S. Pat. No. 4,952,579 (1990), U.S.Pat. No. 4,984,793 (1990), U.S. Pat. No. 4,786,637 (1988). In accordancewith these patents mycophenolate mofetil may be prepared using twostandard esterification methods (see Synthetic Organic Chemistry, R. B.Wagner and H. D. Zook (Wiley, New York), 1956, pages 479 to 532):reaction of mycophenolic chloride with excessive amount of2-morpholinoethanol and condensation using dicyclohexylcarbodiimide(DDC). Esterification via the acid chloride is based on reaction ofexcessive amount of 2-morpholinoethanol with mycophenolic acid chloridethat has been prepared from mycophenolic acid using suitablechlorinating agent (thionylchloride, oxalylchloride etc.). Use of theexcessive amount of 2-morpholinoethanol (up to 3 equivalents), formationof dimmers (about 2%, R¹=H or 2-morpholinoethyl, R²=mycophenolic acid)represents a disadvantage of the two-stage process, there are alsoproblems with colour of the product. Formation of unjustifiable amountof impurities and dicyclohexylurea that may be eliminated from thereaction mixture only by a chromatography is a disadvantage of DCC useas an activating agent.

The U.S. Pat. No. 5,247,083 dated 1993 describes preparation ofmycophenolate mofetil by reflux of mycophenolic acid and2-morpholinoethanol in a suitable solvent or a mixture of solvents underazeotropic water separation. Dichloromethane, benzene, toluene, xyleneand higher hydrocarbons are given in the claims and examples. The mostsuitable solvents are toluene, xylene and their mixture in proportion1:1. A long reaction period necessary to reach sufficient conversion(depending on the solvent used about 60 to 100 hours) and colour of theproduct (light violet crystal) are the disadvantages of this method.

Object of the international application No. WO 00/34503 dated 2000 ismycophenolic acid esterification with 2-morpholinoethanol using enzymecatalysis. This way mycophenolate mofetil may be obtained in high yieldand purity, however, the method may not be used in industry. Within thispatent method of mycophenolic acid esterification by boiling in2-morpholinoethanol without any solvent is described but consideringprice of 2-morpholinoethanol the method is not suitable either.

DISCLOSURE OF THE INVENTION

It was surprising during optimisation of mycophenolate mofetilpreparation by mycophenolic acid direct esterification with2-morpholinoethanol under azeotropic separation of water that thanks touse of dibutyl ether, unlike toluene or xylene, the reaction is slightlyaccelerated. Thanks to the use of higher ethers the problems with thecolour of the product that had been monitored in toluene or xylene wereeliminated. Low solubility of mycophenolate mofetil in higher ethers isalso a favourable property as it makes product isolation fromhigh-boiling solvent easier. That is why the proposed method representsthe most favourable alternative to the method described under the patentU.S. Pat. No. 5,247,083.

Process in accordance with invention solves preparation of mycophenolatemofetil as follows:

Mycophenolic acid is esterified by reflux in ethers (general formulaR³OR⁴, where R³, R⁴=alkyl, aryl), boiling point of which is 120° C. asminimum, under azeotropic separation of water and under use of excessiveamount of 2-morpholinoethanol (1.01 to 3 molar equivalents). Reactiontime is in the range 5 to 50 hours and reaction temperature is higherthan 120° C. depending on the solvent used. The ratio mycophenolic acid:solvent used is in the range 1 g:2 ml to 1 g:5 ml. Conversion is in therange 80 to 98%. After raw product recrystallization mycophenolatemofetil is obtained with purity 99.0% as minimum and yield 70% asminimum.

EXAMPLES

The invention is illustrated with the following examples that however donot limit extent of the patent in any way.

Example 1

Mycophenolate mofetil; use of dibutyl ether as solvent

10 g mycophenolic acid were put in a reaction flask with a reflux coolertogether with 20 ml dibutyl ether. Stirring vigorously the mixture waswarmed up to the temperature of 50 to 60° C. and then 4 ml2-morpholinoethanol were dropped in. The reaction mixture was warmed upto boiling under azeotropic separation of water. After 48 hours themixture was cooled up to the laboratory temperature and diluted with 20ml dichloromethane. The solution was extracted twice with 10 ml 0.5 Maqueous K₂CO₃ and once with 10 ml of water. Then dichloromethane wasdistilled off under vacuum and the suspension was cooled up to 10 to 15°C. Crystallized mycophenolate mofetil was removed by suction andrecrystallized from ethyl acetate. After the removal by suction anddrying the crystals 11 g (78%) mycophenolate mofetil was obtained withpurity>99.0% (HPLC).

Example 2

Mycophenolate mofetil; use of dipentyl ether as solvent

10 g mycophenolic acid were put in a reaction flask with a reflux coolertogether with 20 ml dipentyl ether. Stirring vigorously the mixture waswarmed up to the temperature of 50 to 60° C. and then 4 ml2-morpholinoethanol were dropped in. The reaction mixture was warmed upto boiling under azeotropic separation of water. After 6 hours themixture was cooled up to the laboratory temperature and diluted with 20ml dichloromethane. The solution was extracted twice with 10 ml 0.5 Maqueous K₂CO₃ and once with 10 ml of water. Then dichloromethane wasdistilled off under vacuum and the suspension was cooled up to 10 to 15°C. Crystallized mycophenolate mofetil was removed by suction andrecrystallized from ethyl acetate. After the removal by suction anddrying the crystals 10 g (71%) mycophenolate mofetil was obtained withpurity>99.0% (HPLC).

Example 3

Mycophenolate mofetil; use excess of 2-morfpholinoethanol

10 g mycophenolic acid was put in a reaction flask with a reflux coolertogether with 20 ml dibutyl ether. Stirring vigorously the mixture waswarmed up to the temperature of 50 to 60° C. and then 4,8 ml2-morpholinoethanol was added in. The reaction mixture was warmed up toboiling under azeotropic separation of water. After 15 hours the mixturewas cooled up to the laboratory temperature and diluted with 25 mldichloromethane. The solution was extracted twice with 10 ml of 1%aqueous ammonia and once with 10 ml of water. Then dichloromethane wasdistilled off under vacuum and the suspension was cooled up to 10 to 15°C. Crystallized mycophenolate mofetil was removed by suction andrecrystallized from ethyl acetate. After the removal by suction anddrying the crystals 11,1 g (82%) mycophenolate mofetil was obtained withpurity>99.0% (HPLC).

1. The process of preparation of mycophenolate mofetil by directesterification of mycophenolic acid and 2-morpholinoethanolcharacterized with esterification carried out under boiling in ethers.2. The process according to claim 1, characterized with the use ofethers as solvent of the general formula R³OR⁴, where R³ and R⁴ areindependently alkyl or aryl.
 3. The process according to claim 2,characterized with the use of ethers as solvent of boiling point above120° C.
 4. The process according to claim 1, characterized with the useof 1.01 up to 3.0 molar equivalents of 2-morpholinoethanol.
 5. Theprocess according to claim 3, characterized with the use of dibutyletheras an inert solvent.
 6. The process according to claim 5, characterizedwith the starting temperature of the reaction ranging between 130° C.and 138° C. and the final temperature of the reaction ranging between140° C. and 145° C.
 7. The process according to claim 5, characterizedwith the reflux time ranging from 30 to 80 hours.
 8. The processaccording to claim 5, characterized with the ratio of mycophenolic acidto dibutylether ranging from 1 g/2 ml to 1 g/5 ml.